Pressure sensor

ABSTRACT

The pressure sensor comprises two supporting bodies ( 10,11 ) with plane supporting surfaces ( 12,13 ) between which a hose ( 14 ) is flattened. For measuring the internal pressure of the hose ( 14 ), a web ( 17 ) displaceable in a gap ( 16 ) is arranged at a supporting body ( 10 ), said web pressing against the plane surface of the flattened hose ( 14 ) and being supported on a force sensor ( 19 ). Thus, the deformation forces generated upon compressing the hose are eliminated for the measurement of pressure.

FIELD OF THE INVENTION

[0001] The invention relates to a pressure sensor comprising a hose for passing a fluid, two supporting bodies deforming the cross-section of the hose and a force sensor reacting to the internal pressure of the hose.

BACKGROUND ART

[0002] In medical technics, hoses are used to supply liquid to a patient by infusion or to take liquid from a patient or to convey liquid between apparatuses or machines. In doing so, it is necessary to detect a hose occlusion such as it occurs, for example, if the hose is kinked. Further, it is often necessary to limit the internal pressure of a hose.

[0003] From DE 40 13 403 C2, a pressure sensor is known where the hose is compressed between two supporting bodies. The one supporting body forms a stationary abutment and the other supporting body is movable and supported by a force sensor. The force sensor detects the force acting upon the hose. This force is counteracted by the restoring force of the hose and the internal pressure of the hose. To measure the internal pressure with sufficient precision, the utilized hose and its restoring ability have to be known. For detecting the material properties of the hose, a time-consuming comparison measurement is performed. As a rule, however, the material properties of the hose depend on the temperature so that different comparison measurements would have to be conducted at different operational temperatures. The deformation force required for deforming the hose, which is particularly high in the border zones of the hose, superimposes the pressure signal up to the factor 10. Therefore, combined measurements of both forces are very incorrect. Moreover, the deformation force is not constant in time over the period of service of the hose.

[0004] A similar pressure sensor where a measurement of the hose properties is made first before the signals of the force sensor are evaluated is described in DE 38 38 689 C1. Here, the restoring forces of the hose are also superimposed by the force generated by the internal hose pressure.

[0005] It is the object of the invention to provide a pressure sensor the measuring signals of which are largely independent of the utilized hose and the placement duration thereof.

[0006] This object is solved, according to the invention, with the features set forth in claim 1. Accordingly, at least one of the supporting bodies includes a force transmission means that is movable relative to this supporting body and presses against the hose with one end and against the force sensor with the other end.

SUMMARY OF THE INVENTION

[0007] The force transmission means should be spaced from the two bending portions of the hose as far as possible. Particularly, it has a width that amounts to maximally 25% of the lumen (width) of the hose deformed by the supporting bodies, and particularly maximally 15%.

[0008] Thereby, it is achieved that the deformation forces of the hose are received by the supporting bodies and substantially kept away from the force sensor. The force sensor is decoupled from the supporting bodies, i.e., it does not react to forces generated by loading the supporting bodies. Particularly, the supporting bodies provide for the support in the two curved portions of the flattened hose. The force transmission means transmits the force from the central portion of the flattened hose to the force sensor. Here, only deformations of the central portion caused by the internal pressure of the hose have an effect.

[0009] Preferably, the force sensor is a sensor with a particularly low excursion, the maximum excursion amounting to less than 1 mm. Thereby, the additional deformation caused by the internal pressure of the hose is kept small and the influence of the hose material upon the measuring result is limited.

[0010] For supporting the force transmission means, several force sensors may be provided which are arranged so as to be distributed in longitudinal direction of the hose.

[0011] Preferably, the force transmission means consists of a web extending in longitudinal direction of the hose. This web may be a solid web or may also consist of an incompressible gel. What is important is that the web is movable relative to the supporting body through which it extends and engages the flattened hose in its central portion so that it is largely freed from the forces generated by compressing the hose.

[0012] Preferably, the supporting bodies have plane supporting surfaces, but it is also possible to provide a trough in the one supporting body and to provide the other supporting body with a level or slightly concave supporting surface.

[0013] Since the deformation forces are received by the supporting bodies, the central portion of the hose rests on the force transmission means like a membrane. If pressure is generated in the hose, the pressure force proportional to the cross-sectional area of the gap is transferred to the force sensor via the web. From the cross-sectional area A of the web and the force F, the pressure P in the hose can be calculated as P=F×A. The force signal is evaluated in a microprocessor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Hereinafter, embodiments of the invention will be explained in detail with reference to the drawings.

[0015] In the Figures:

[0016]FIG. 1 shows a schematic perspective sectional view of a first embodiment of the pressure sensor with a solid web, and

[0017]FIG. 2 shows, in the same manner as FIG. 1, a pressure sensor with an incompressible gel.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0018] The pressure sensor according to FIG. 1 comprises two plate-shaped supporting bodies 10,11 having a plane supporting surface 12,13 each. Between the parallel supporting surfaces 12,13, the hose 14 is flattened. To this end, one of the supporting bodies 10,11 is movable towards the other supporting body.

[0019] The hose 14 consists of a flexible material that is elastic and thus has a restoring ability. In the uncompressed state, the cross-section of the hose 14 is round. In the flattened state of the hose, the hose cross-section has a longitudinal shape as illustrated in FIG. 1. In the hose lumen 15, there is a liquid, for example an infusion solution, which is supplied to a patient.

[0020] Through the supporting body 10, a longitudinally extending gap 16 extends which is arranged in the central portion of the flattened hose 14. The hose 14 is held in a defined position between the supporting bodies 10,11 by (non-illustrated) side walls. The gap 16 extends through the thickness of the supporting body 10. In the gap 16, a force transmission means in the form of a web 17 is arranged. The web 17 is displaceable transversely to the supporting body 10. It extends in longitudinal direction of the hose 14. At the one end of the web 17, a foot 18 is provided which presses against a force sensor 19. The force sensor 19 is rigidly mounted to the supporting body 10 by (non-illustrated) locking means. The force sensor 19, for example, comprises expansion measuring strips that are connected to form a bridge circuit and generate an electrical signal that is proportional to the force F acting upon the force sensor 19.

[0021] A corresponding force sensor 19 may also be arranged at the opposite end of the web 17 where a further foot corresponding to the foot 18 is provided.

[0022] The web 17 is a solid body which, for example, consists of a rigid plate. The upper end 20 of the web 17 presses directly against the periphery of the hose 14 in the central portion of the hose flattened between the supporting bodies 10,11, where the hose wall extends linearly.

[0023] In the embodiment of FIG. 2, the one supporting body 10 is also provided with a longitudinally extending gap 16, and at the side of the supporting body 10 facing away from the hose 14, a force sensor 19 covering the gap 16 is mounted. The gap 16 is filled with a force transmission means consisting of an incompressible gel 22. At one end, this gel 22 presses against the straight portion of the wall of the flattened hose 14 and at the other end, it presses against the pressure-sensitive surface of the force sensor 19. The gel 22 may be confined by deformable membranes covering the gap 16 at the upper and under surfaces thereof. The gel 22 forms a force transmission means transmitting the deformation of the hose wall, which depends on the internal pressure, to the force sensor 19.

[0024] In both cases, only the hose deformation at the gap 16 is evaluated for generating the force signal when the pressure in the hose 14 changes. The force sensor 19 generates an electrical signal that is proportional to the internal pressure of the hose with high precision.

[0025] In the embodiment of the invention, a pressure of 1 bar corresponds to a force of 100,000 N/m5. With a surface area of the gap of 10 mm×2 mm, this results in 2 N/bar. In this case, the proportionality factor amounts to 0.5. 

I claim:
 1. A pressure sensor comprising a hose for passing a fluid, two supporting bodies deforming the cross-section of the hose, and a force sensor reacting to the internal pressure of the hose, characterized in that at least one of the supporting bodies includes a force transmission means which extends over less than 25% of the lumen of the hose deformed by the supporting bodies, which is movable relative to this supporting body and presses against the hose with one end and against the force sensor with the other end.
 2. The pressure sensor according to claim 1, characterized in that the force transmission means is arranged in a gap extending through the supporting body.
 3. The pressure sensor according to claim 2, characterized in that the gap extends in longitudinal direction of the hose and in the middle of the cross-section thereof.
 4. The pressure sensor according to claim 1, characterized in that the force sensor is mounted to the supporting body including the force transmission means.
 5. The pressure sensor according to claim 1, characterized in that the force transmission means consists of an elongate web.
 6. The pressure sensor according to claim 5, characterized in that the web is a solid web.
 7. The pressure sensor according to one of the preceding claims, characterized in that the force transmission means consists of an incompressible gel. 